Rubber mountings of this general kind are used for mounting drive units in vehicles of all types. In the mounting of internal combustion engines in motor vehicles, a number of considerations are applicable. Thus, on the one hand, in order to avoid the transmission of noise it is desirable to provide the softest possible mounting with a low level of natural damping, which however, allows the movements of the engine, which are generated by, for instance, travel over the road surface, to become very great and almost go into a condition of undamped oscillation. On the other hand, substantial movements of the engine can be reduced by using hard engine mountings or separate vibration dampers, which, however, in turn results in a considerable amount of noise being transmitted to the vehicle body.
Rubber mountings generally of the above described kind are known (for example, published European patent application No. 27,751), which suffer from the disadvantage that the mounting has inadequate damping or damping over a narrow band, and inadequate dynamic decoupling of the small vibrations or oscillations of the engine. The decoupling surface, which is small in comparison with the outside diameter, provides an inadequate dynamic spring rate with which severe increases or overloads occur while still within the range which is important from the point of view of noise transmission. It is therefore not possible to achieve optimum insulation in respect of the transmission of noise from the engine to the body, in the range of about 20 to 200 Hz.
Also known are engine mountings (for example, European published application No. 12,638) in which the chambers are arranged concentrically with respect to each other and which generally have a good damping action in the low-frequency range. The disadvantage there, however, is that dynamic hardening of this known engine mounting occurs at higher frequencies of oscillation. The engine mounting therefore scarcely has any capability of insulation in respect of the high-frequency noise vibrations which are thus disadvantageously transmitted from the engine to the vehicle body.
Taking the above described art as its starting point, an object of the present invention is to provide a simple and effective rubber mounting which not only keeps low and provides adequate damping in respect of the engine vibrations which are stimulated by travel over the road surface and which originate from the engine when starting up and stopping, in the natural frequency range of the engine, while avoiding shock or impact noises when the damping action occurs, but which also provides for optimum insulation in respect of the transmission of noise from the engine to the body in the range of from about 20 to 200 Hz, wherein a linear dynamic spring rate is to be provided in that frequency range.
To achieve the foregoing object, the present invention provides that the rigid partitioning wall which has the flow passage is arranged radially inwardly of an elastic, axially movable diaphragm which is fixedly and sealingly clamped at its outer periphery.
It is advantageous for the partitioning wall to be held by the axially movable diaphragm so that it is possible in a particularly simple manner to provide for decoupling of the high-frequency, low-amplitude noise vibration. In addition, one of the two chambers serves in the operating range as an elastically deformable compensating chamber which increases in volume in an almost pressureless mode, wherein the peripheral wall of the chamber which is formed as the compensating chamber is not in the form of a rubber-elastic spring element, like the other chamber, but is in the form of a concertina-type means. The partitioning wall in conjunction with the diaphragm acts as a decoupling diaphragm which is combined with the annular flow passage that provides a particularly good damping action, so that an important advantage is to be considered as being the fact that a combination of a high damping action in the desired low-frequency and large-amplitude range and good noise insulation at high oscillation frequencies and low amplitudes is achieved, with particularly simple means. The decoupling surface area of the rigid partitioning wall, which is large in relation to the outside diameter of the mounting, ensures a linear dynamic spring rate at a low level.
Another advantageous feature provides that the outside periphery of the partitioning wall at least partially overlaps the diaphragm on its underside and/or its top side and that, starting from the clamping location radially inwardly of the overlapping peripheral portions of the partitioning wall, the spacing of the travel limiting surface or surfaces from the diaphragm increases in a radially outward direction. The travel limiting surfaces are, of course, provided by the overlapping portions of the partitioning wall radially outwardly of the clamping location. An advantage with that embodiment is that the travel limiting surfaces which gradually move apart from each other ensure, both in regard to the diaphragm for suspending the decoupling means and also in regard to the central rigid partitioning wall, that, when the damping action occurs at large amplitudes, shock or impact noises are avoided. Depending on the particular characteristics desired for a particular application, the travel limiting surface may be of a curved configuration, or a configuration which is made up of a curve and a straight line, or a straight-line configuration.
In accordance with another advantageous embodiment of the invention, the partitioning wall has projections which are uniformly distributed over its periphery. By virtue of the provision of such projections, interruptions are provided at the outside contour of the partitioning wall, and, possibly in conjunction with a grooved structure on the corresponding surface of the diaphragm, the arrangement provides that the curve of the dynamic spring rate, in relation to frequency, is corrected, for this arrangement avoids harmful liquid displacement and liquid suction effects.
An advantageous embodiment provides that the dimensions of the annular flow passage are selected in accordance with the following relationship: L/.sqroot.F.ltoreq.20, wherein L denotes the length of the flow passage and F denotes the cross-sectional area thereof.
In accordance with a particularly advantageous embodiment of the invention, the outer periphery of the diaphragm, or the outer periphery of a member secured to the diaphragm, is clamped in the connecting flange of the chambers. The diaphragm is advantageously sealingly connected at its outer periphery to a rigid clamping ring which is fixedly clamped at the connecting flange, the diaphragm engaging around the clamping ring at both faces thereof, forming axial beads. This arrangement, being of a simple design configuration, provides an advantageous configuration in respect of the axially movable partitioning wall which contains the annular flow passage. It will be appreciated that, in that arrangement, the rigid partitioning wall and the diaphragm are matched to each other in such a way as to provide for optimum decoupling of the high-frequency, low-amplitude noise vibrations.
In accordance with a particularly advantageous embodiment of the invention, the rigid partitioning wall is radially divided at its center, and, for sealingly receiving the diaphragm, the travel limiting surfaces have an internal enlargement for form-lockingly or positively receiving the diaphragm at the clamping location. The diaphragm may be provided with a reinforcing ring in the region of the clamping location.